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1.
Tunnel excavation at Äspö Island, Sweden, has caused severe groundwater disturbance, gradually extending deeper into the tunnel as present-day Baltic seawater intrudes through fractures connecting to the surface. However, the paleo-hydrogeochemical conditions have remained in the deep highly saline waters that have avoided mixing. A correlation has been observed between dissolved 4He concentration and Cl− ion concentration, measured every two years from 1995 to 2001 at Äspö. Groundwater mixing conditions can be examined by the correlations between 1/Cl, 36Cl/Cl, and 3H concentrations. Subsurface production is responsible for the majority of the 36Cl and excess dissolved 4He of interstitial groundwater in fractures. The secular equilibrium ratio of 36Cl/Cl in rock was theoretically estimated to be (5.05 ± 0.82) × 10−14 based on the neutron flux intensity, a value comparable to the measured 36Cl/Cl ratio in rock and groundwater. The degassing crustal 4He flux was estimated to be 2.9 × 10−8  1.3 × 10−6 (ccSTP/cm2a) using the HTO diffusion coefficient for the Äspö diorite. The 4He accumulation rate ranges from 6.8 × 10−10 (for the in situ accumulation rate) to 7.0 × 10−9 (ccSTP/(gwater · a) considering both 4He in situ production and the degassing flux, assuming 4He is accumulated constantly in groundwater. By comparing the subsurface 36Cl increase with 4He concentrations in groundwater, the 4He accumulation rate was determined from data for groundwater arriving at the secular equilibrium of 36Cl/Cl. The 4He accumulation rate was found to be (1.83 ± 0.72) × 10−8 ccSTP/(gwater · a) without determining the magnitude of degassing 4He flux.  相似文献   

2.
The Yueshan mineral belt is geotectonically located at the centre of the Changjiang deep fracture zone or depression of the lower Yangtze platform. Two main types of ore deposits occur in the Yueshan orefield: Cu–Au–(Fe) skarn deposits and Cu–Mo–Au–(Pb–Zn) hydrothermal vein-type deposits. Almost all deposits of economic interest are concentrated within and around the eastern and northern branches of the Yueshan dioritic intrusion. In the vicinity of the Zongpu and Wuhen intrusions, there are many Cu–Pb–Zn–Au–(S) vein-type and a few Cu–Fe–(Au) skarn-type occurrences.Fluid inclusion studies show that the ore-forming fluids are characterised by a Cl−(S)–Na+–K+ chemical association. Hydrothermal activity associated with the above two deposit types was related to the Yueshan intrusion. The fluid salinity was high during the mineralisation processes and the fluid also underwent boiling and mixed with meteoric water. In comparison, the hydrothermal activity related to the Zongpu and Wuhen intrusions was characterised by low salinity fluids. Chlorine and sulphur species played an important role in the transport of ore-forming components.Hydrogen- and oxygen-isotope data also suggest that the ore-forming fluids in the Yueshan mineral belt consisted of magmatic water, mixed in various proportions with meteoric water. The enrichment of ore-forming components in the magmatic waters resulted from fluid–melt partitioning. The ore fluids of magmatic origin formed large Cu–Au deposits, whereas ore fluids of mixed magmatic-meteoric origin formed small- to medium-sized deposits.The sulphur isotopic composition of the skarn- and vein-type deposits varies from − 11.3‰ to + 19.2‰ and from + 4.2‰ to + 10.0‰, respectively. These variations do not appear to have been resulted from changes of physicochemical conditions, rather due to compositional variation of sulphur at the source(s) and by water–rock interaction. Complex water–rock interaction between the ore-bearing magmatic fluids and sedimentary wall rocks was responsible for sulphur mixing. Lead and silicon isotopic compositions of the two deposit types and host rocks provide similar indications for the sources and evolution of the ore-forming fluids.Hydrodynamic calculations show that magmatic ore-forming fluids were channelled upwards into faults, fractures and porous media with velocities of 1.4 m/s, 9.8 × 10− 1 to 9.8 × 10− 7 m/s and 3.6 × 10− 7 to 4.6 × 10− 7 m/s, respectively. A decrease of fluid migration velocity in porous media or tiny fractures in the contact zones between the intrusive rocks and the Triassic sedimentary rocks led to the deposition of the ore-forming components. The major species responsible for Cu transport are deduced to have been CuCl, CuCl2−, CuCl32− and CuClOH, whereas Au was transported as Au2(HS)2S2−, Au(HS)2−, AuHS and AuH3SiO4 complexes. Cooling and a decrease in chloride ion concentration caused by fluid boiling and mixing were the principal causes of Cu deposition. Gold deposition was related to decrease of pH, total sulphur concentration and fO2, which resulted from fluid boiling and mixing.Geological and geochemical characteristics of the two deposit types in the Yueshan mineral belt suggest that there is a close genetic relationship with the dioritic magmatism. Geochronological data show that the magmatic activity and the mineralisation took place between 130 and 136 Ma and represent a continuous process during the Yanshanian time. The cooling of the intrusions and the mineralisation event might have lasted about 6 Ma. The cooling rate of the magmatic intrusions was 80 to 120 °C my− 1, which permitted sufficient heat supply by magma to the ore-forming system.  相似文献   

3.
The release of irradiation-produced noble gas isotopes (38ArCl, 80KrBr, 128XeI and 39ArK) during in vacuo crushing scapolite has been investigated and is compared to quartz. Three thousand crushing strokes released 98% of fluid inclusion-hosted noble gas from quartz. In comparison, 3000 crushing strokes released only 4% of the lattice-hosted 38ArCl from a scapolite gem. In vacuo crushing released lattice Ar preferentially relative to lattice Kr or Xe and prolonged crushing released 88% of the lattice-hosted noble gas in 96,000 crushing strokes. We suggest fast diffusion pathways generated by crushing are an important noble gas release mechanism and we demonstrate two applications of prolonged in vacuo crushing on irradiated scapolite.Firstly, scapolite molar Br/Cl and I/Cl values are shown to vary over a similar range as crustal fluids. The Cl-rich scapolite gem from Hunza, Pakistan has Br/Cl of 0.5–0.6 × 10−3 and I/Cl values of 0.3–2 × 10−6, that are similar to fluids that have dissolved evaporites. In contrast, three out of four skarn-related scapolites from the Canadian Grenville Province have molar Br/Cl values of 1.5–2.4 × 10−3, and I/Cl values of 11–24 × 10−6, that are broadly consistent with skarn formation by magmatic fluids. The fourth Grenvillian scapolite, with only 0.02 wt% Cl, has an exceptionally elevated molar Br/Cl value of up to 54 × 10−3 and I/Cl of 284 × 10−6. It is unclear if these values reflect the composition of fluids formed during metamorphism or preferential incorporation of Br and I in Cl-poor meionitic scapolite.Secondly, the Grenvillian scapolites give plateau ages of between 830 Ma and 400 Ma. The oldest ages post-date regional skarn formation by 200 Myr, but are similar to feldspar cooling ages in the Province. The age variation in these samples is attributed to a combination of factors including variable thermal history and the presence of mineral sub-grains in some of the samples. These sub-grains control the release of 39ArK, 38ArCl and 40Ar* during in vacuo crushing as well as the samples 40Ar* retentivity in nature. Scapolite is suggested as a possible analogue for K-feldspar in thermochronologic studies.  相似文献   

4.
The Daduhe gold field comprises several shear-zone-controlled Tertiary lode gold deposits distributed at the eastern margin of the Tibetan Plateau. The deposits are hosted in a Precambrian granite–greenstone terrane within the Yangtze Craton. The gold mineralization occurs mainly as auriferous quartz veins with minor sulphide minerals. Fluid inclusions in pyrite have 3He/4He ratios of 0.16 to 0.86 Ra, whereas their 40Ar/36Ar ratios range from 298 to 3288, indicating a mixing of fluids of mantle and crust origins. The δ34S values of pyrite are of 0.7–4.2‰ (n = 12), suggesting a mantle source or leaching from the mafic country rocks. δ18O values calculated from hydrothermal quartz are between − 1.5‰ and + 6.0‰ and δD values of the fluids in the fluid inclusions in quartz are − 39‰ and − 108‰. These ranges demonstrate a mixing of magmatic/metamorphic and meteoric fluids. The noble gas isotopic data, along with the stable isotopic data suggest that the ore-forming fluids have a dominantly crustal source with a significant mantle component.  相似文献   

5.
The Qaleh-Zari copper deposit, located in South Khorasan in the Central Lut region of Iran, is a polymetallic vein deposit with major amounts of Cu, Au, Ag and minor amounts of Pb, Zn and Bi. Mineralization occurs in a series of NW–SE trending fault planes and breccia zones in Paleogene andesitic to basaltic volcanic rocks. Argillization, sericitization and propylitization characterize alteration halos bordering mineral veins. The main ore minerals are chalcopyrite, pyrite, galena and sphalerite, with quartz, calcite and minor chlorite as the main gangue phases. Microthermometric measurements of fluid inclusions in cogenetic quartz indicate homogenization temperatures between 160 and 300 °C and salinities from 1 to 4 wt% NaCl equiv. Boiling occurred in the mineralising fluids at 160–1000 m below the paleo-water table at pressures of approximately 15−80 bar at various stages in the formation of the ore body. The wide range of pressures and temperatures reflects the multi-stage nature of the mineralization at Qaleh-Zari. The δ18O values in quartz (relative to SMOW) and δ34S values in chalcopyrite and galena (relative to CDT) range from 6.5 to 7.5‰ and 0.0–1.5‰ (mean: 7.0‰), respectively. At 300 °C, calculated fluid δ18O values are close to 0‰. These data suggest a magmatic origin for sulfur and a surficial origin for the mineralizing fluid. Mineralization at Qaleh-Zari is interpreted as epithermal and low-sulfidation in style and was probably related to a deep-seated magmatic system. Ore deposition was the result of boiling, cooling and pressure reduction.  相似文献   

6.
The isotopic composition of Fe was determined in water, Fe-oxides and sulfides from the Tinto and Odiel Basins (South West Spain). As a consequence of sulfide oxidation in mine tailings both rivers are acidic (1.45 < pH < 3.85) and display high concentrations of dissolved Fe (up to 420 mmol l− 1) and sulphates (up to 1190 mmol l− 1).The δ56Fe of pyrite-rich samples from the Rio Tinto and from the Tharsis mine ranged from − 0.56 ± 0.08‰ to + 0.25 ± 0.1‰. δ56Fe values for Fe-oxides precipitates that currently form in the riverbed varied from − 1.98 ± 0.10‰ to 1.57 ± 0.08‰. Comparatively narrower ranges of values (− 0.18 ± 0.08‰ and + 0.21 ± 0.14‰) were observed in their fossil analogues from the Pliocene–Pleistocene and in samples from the Gossan (the oxidized layer that formed through exposure to oxygen of the massive sulfide deposits) (− 0.36 ± 0.12‰ to 0.82 ± 0.07‰). In water, δ56Fe values ranged from − 1.76 ± 0.10‰ to + 0.43 ± 0.05‰.At the source of the Tinto River, fractionation between aqueous Fe(III) and pyrite from the tailings was less than would be expected from a simple pyrite oxidation process. Similarly, the isotopic composition of Gossan oxides and that of pyrite was different from what would be expected from pyrite oxidation. In rivers, the precipitation of Fe-oxides (mainly jarosite and schwertmannite and lesser amounts of goethite) from water containing mainly (more than 99%) Fe(III) with concentrations up to 372 mmol l− 1 causes variable fractionation between the solid and the aqueous phase (− 0.98‰ < Δ56Fesolid–water < 2.25‰). The significant magnitude of the positive fractionation factor observed in several Fe(III) dominated water may be related to the precipitation of Fe(III) sulphates containing phases.  相似文献   

7.
A case study of three springs in Switzerland is used to demonstrate the value of geochemical time-series data as a powerful tool to study the dynamics of groundwater systems. Values of repeatedly measured parameters revealed intermixings of two water types: (a) a 29°C water, circulating to a depth of 1100 m and containing approximately 700 mg/l Ca, 2000 mg/l SO4, 700 mg/l HCO3, 20 mg/l of Na and Cl, 6 mg/l Fe, at least 47 mg/l SiO2, and with an isotopic composition of δD = − 73.0‰ and δ18 O = −10.9‰, and (b) a 12°C or colder water, shallow, and of a post-1953 age, containing 420 mg/l TDI or less, very low in Na and Cl (4 mg/l or less), isotopic values of δD = −71.0‰ and δ18 O = −10.5‰ and tritium as in recent (post-bomb) precipitation.  相似文献   

8.
Located at western portion of northern margin of North China craton, the Baotou–Bayan Obo district is one of the most important Fe–REE–Nb and Au metallogenic provinces in China. Presently, about 52 gold deposits and prospects have been discovered, explored and mined, among which Shibaqinhao, Laoyanghao, Houshihua, Saiyinwusu, Wulashan and Donghuofang are the most important ones. All these gold occurrences can be subdivided into three groups (or types) according to its host rocks: (1) hosted by Archean high-grade metamorphic rocks; (2) hosted by Proterozoic sedimentary rocks; (3) hosted by or related to Hercynian alkaline intrusive rocks. The first group contains the Shibaqinhao, Laoyanghao and Houshihua gold deposits. Gold mineralization at these three deposits occurs within Archean amphibolite, gneiss and granulite as gold-bearing quartz veins and veinlet groups containing native gold, electrum, pyrite and chalcopyrite. The Saiyinwusu deposit belongs to the second group, and occurs within Proterozoic sandstone, quartzite and carbonaceous slate as quartz veins and replacement bodies along the fracture zones. Pyrite, marcasite, arsenopyrite, native gold and electrum are identified. The third group includes the Wulashan, Donghuofang and Luchang deposits. Gold mineralization at these three deposits occurs predominantly within the Hercynian alkaline syenite or melagabbro stocks and dyke swarms or along their contacts with Archean metamorphic wall rocks as K-feldspar–quartz veins, dissemination and veinlets. Pyrite, galena, chalcopyrite, native gold and calaverite are major metallic minerals.δ34S value of sulfides (pyrite, galena and pyrrhotite) separates from groups 1 and 2 varies from −4.01‰ to −0.10‰ and −3.01‰ to 2.32‰, respectively. δ34S values of Archean and Proterozoic metamorphic wall rocks for groups 1 and 2 deposits range from −20.2‰ to −17.0‰ and −15.8‰ to −16.2‰, respectively. The values are much lower than their hosted gold deposits. All these pyrite separates from Hercynian alkaline intrusions associated with the gold deposits show positive δ34S values of 1.3‰ to 4.8‰, which is higher than those Precambrian metamorphic wall rocks and their hosted gold deposits. δ34S values of the sulfides (pyrite and galena) from the Donghuofang and Wulashan deposits (group 3) increase systematically from veins (−14.8‰ to −2.4‰) to the Hercynian alkaline igneous wall rocks (2.8‰ to 4.8 ‰). All of these deposits in groups 1, 2 and 3 show relatively radiogenic lead isotopic compositions compared to mantle or lower crust curves. Most lead isotope data of sulfides from the gold ores plot between the Hercynian alkaline intrusions and Precambrian metamorphic wall rocks. Data are interpreted as indicative of a mixing of lead from mantle-derived alkaline magma with lead from Precambrian metamorphic wall rocks.Isotopic age data, geological and geochemical evidence suggest that the ore fluids for the groups 1 and 2 deposits were generated during the emplacement of the Hercynian alkaline syenite and mafic intrusions. The Hercynian alkaline magma may provide heat, volatiles and metals for these groups 1 and 2 deposits. Evolved metamorphic fluids produced by the devolatilization, which circulated the wall rocks, were also progressively involved in the alkaline magmatic hydrothermal system, and may have dominate the ore fluids during late stage of ore-forming processes. Most of these gold deposits hosted by Archean high-grade metamorphic rocks occur at or near the intersections of the NE- and E–W-trending fracture systems. The ore fluid of the group 3 deposits may have resulted from the mixing of Hercynian alkaline magmatic fluids and evolved meteoric waters. The deposits are believed to be products of Hercynian alkaline igneous processes along deep-seated fault zones within Archean terrain.  相似文献   

9.
The Cobre–Babilonia vein system formed during a single major hydrothermal stage and is part of the Taxco district in Guerrero, southern Mexico. Homogenization and ice melting temperatures range from 160 to 290 °C and from − 11.6 to − 0.5 °C, respectively. We determined an approximate thermal gradient of 17 to 20 °C per 100 m using fluid inclusions. A thermal peak marked by the 290 °C isotherm is interpreted as a major feeder channel to the veins. The highest content of Zn + Pb in ore coincides with the 220 and 240 °C isotherms. Salinities of mineralizing fluids range from 0.8 to 15.6 wt.% NaCl equiv, and are distributed in two populations that can be related with barren or ore-bearing vein sections, with 0.8 to 6 wt.% NaCl equiv and 7 to 15.6 wt.% NaCl equiv, respectively. δ13C and δ18O water values from calcite from the Cobre–Babilonia vein system and the Esperanza Vieja and Guadalupe mantos range − 5.4‰ to − 10.4‰ and 9.9‰ to 13.4‰, respectively. δ34S values range from 0‰ to 3.2‰ and − 0.7‰ to − 4.3‰ in sphalerite, − 4‰ to 0.9‰ in pyrite, and − 1.4‰ to − 5.5‰ in galena. Both fluid inclusion and stable isotope data are compatible with magmatic and meteoric sources for mineralizing fluids. Also, sulfur isotope compositions suggest both magmatic and sedimentary sources for sulfur.  相似文献   

10.
Elemental (C/N ratio) and C isotope composition (δ13C) of particulate organic C (POC) and organic C content (OC) of total suspended solids (TSS) were determined for two subtropical karstic tributaries of the Yangtze River, the Wujiang (the eighth largest tributary) and Yuanjiang (the third largest tributary). For the latter, two headwaters, the karstic Wuyanghe and non-karstic Qingshuijiang were studied. The Wujiang catchment is subject to intensive land use, has low forest coverage and high soil erosion rate. The δ13C of POC covered a range from −30.6‰ to −24.9‰, from −27.6‰ to −24.7‰, and from −26.2‰ to −23.3‰ at the low-water stage, while at the high-water stage varied in a span between −28.6‰ and −24.4‰, between −27.7‰ and −24.5‰, and between −27.6‰ and −24.2‰ for the Wujiang, Wuyanghe, and Qingshuijiang, respectively. The combined application of C isotopes, C/N ratio, OC, and TSS analyses indicated that catchment soil was the predominant source of POC for the Wujiang while for the Wuyanghe and Qingshuijiang, in-stream processes supplied the main part of POC in winter and summer. A significant increase in δ13C value (1.4‰) of POC was found in the Wujiang during summer, and was attributed to the enhanced soil erosion of the dry arable uplands close to the riverbanks of the main channel. Based on a conservative estimate, POC fluxes were 3.123 × 1010, 0.084 × 1010, and 0.372 × 1010 g a−1 while export rates of POC were 466, 129, and 218 mg m−2 a−1 for the Wujiang, Wuyanghe, and Qingshuijiang, respectively. The POC export rate for the karstic Wujiang, with intensive land use, was 2–3 higher than that of the karstic Wuyanghe or of the non-karstic Qingshuijiang where soil erosion was minor. Such high values imply rapid degradation of related karstic ecosystems impacted by intensive land use activities, and pose a potential threat to the health of the Three Gorges Reservoir.  相似文献   

11.
The Changkeng Au and Fuwang Ag deposits represent an economically significant and distinct member of the Au–Ag deposit association in China. The two deposits are immediately adjacent, but the Au and Ag orebodies separated from each other. Ores in the Au deposit, located at the upper stratigraphic section and in the southern parts of the orefield, contain low Ag contents (< 11 ppm); the Ag orebodies, in the lower stratigraphic section, are Au-poor (< 0.2 ppm). Changkeng is hosted in brecciated cherts and jasperoidal quartz and is characterized by disseminated ore minerals. Fuwang, hosted in the Lower Carboniferous Zimenqiao group bioclastic limestone, has vein and veinlet mineralization associated with alteration comprised of quartz, carbonate, sericite, and sulfides. Homogenization temperatures of fluid inclusions from quartz veinlets in the Changkeng and Fuwang deposits are in the range of 210 ± 80 °C and 230 ± 50 °C, respectively. Salinities of fluid inclusions from the two deposits range from 1.6 to 7.3 wt.% and 1.6 to 2.6 wt.% equiv. NaCl, respectively. The δDH2O, δ18OH2O, δ13CCO2 and 3He/4He values of the fluid inclusions from the Changkeng deposit range from − 80‰ to − 30‰, − 7.8‰ to − 3.0‰, − 16.6‰ to − 17.0‰ and 0.0100 to 0.0054 Ra, respectively. The δDH2O, δ18OH2O, δ13CCO2 and 3He/4He values of fluid inclusions from the Fuwang deposit range from − 59‰ to − 45‰, − 0.9‰ to 4.1‰, − 6.7‰ to − 0.6‰ and 0.5930 to 0.8357 Ra, respectively. The δDH2O, δ18OH2O, δ13CCO2 and 3He/4He values of the fluid inclusions suggest the ore fluids of the Changkeng Au-ore come from the meteoric water and the ore fluids of the Fuwang Ag-ore are derived from mixing of magmatic water and meteoric water. The two deposits also show different Pb-isotopic signatures. The Changkeng deposit has Pb isotope ratios (206Pb/204Pb: 18.580 to 19.251, 207Pb/204Pb: 15.672 to 15.801, 208Pb/204Pb: 38.700 to 39.104) similar to those (206Pb/204Pb: 18.578 to 19.433, 207Pb/204Pb: 15.640 to 15.775, 208Pb/204Pb: 38.925 to 39.920) of its host rocks and different from those (206Pb/204Pb: 18.820 to 18.891, 207Pb/204Pb: 15.848 to 15.914, 208Pb/204Pb: 39.579 to 39.786) of the Fuwang deposit. The different signatures indicate different sources of ore-forming material. Rb–Sr isochron age (68 ± 6 Ma) and 40Ar–39Ar age (64.3 ± 0.1 Ma) of the ore-related quartz veins from the Ag deposit indicate that the Fuwang deposit formed during the Cenozoic Himalayan tectonomagmatic event. Crosscutting relationships suggests that Au-ore predates Ag-ore. The adjacent Changkeng and Fuwang deposits could, however, represent a single evolved hydrothermal system. The ore fluids initially deposited Au in the brecciated siliceous rocks, and then mixing with the magmatic water resulted in Ag deposition within fracture zones in the limestone. The deposits are alternatively the product of the superposition of two different geological events. Age evidence for the Fuwang deposit, together with the Xiqiaoshan Tertiary volcanic-hosted Ag deposit in the same area, indicates that the Pacific Coastal Volcanic Belt in the South China Fold Belt has greater potential for Himalayan precious metal mineralization than previous realized.  相似文献   

12.
Groundwaters and surface water in the Shihongtan sandstone-hosted U ore district, Xinjiang, NW China, were sampled and analyzed for their major-, and trace element concentrations and oxygen, hydrogen, boron and strontium isotope compositions in order to assess the possible origins of the waters and water–rock interactions that occurred in the deep aquifer system. The waters in the study district have been grouped into three hydrochemical facies: Facies 1, potable spring-water, is a pH neutral (7.0), Na–Ca–HCO3 type water with low total dissolved solids (TDS; 0.2 g/l, fresh) and has δ18O of − 8.3‰, δD of − 48.2‰,δ11B of 1.5‰, and 87Sr/86Sr of 0.70627. Facies 2 groundwaters are mildly acidic to mildly alkaline (pH of 6.5–8.0, mean 7.3), Na–Ca–Mg–Cl–SO4 type waters with moderate TDS (8.2 g/l–17.2 g/l, mean 9.3 g/l, brackish) and haveδ18O values in the − 5.8‰ to − 9.3‰ range (mean − 8.1‰), δD values in the − 20.8‰ to − 85.5‰ range (mean − 47.0‰),δ11B values in the + 9.5‰ to + 39.1‰ range (mean + 17.1‰), and 87Sr/86Sr values in the 0.70595 to 0.70975 range (mean 0.70826). Facies 3, Aiting Lake water, is a mildly alkaline (pH = 7.4), Na–Ca–Mg–Cl–SO4 type water with the highest TDS (249.1 g/l, brine) and has δ18O of − 2.8‰, δD of − 45.8‰,δ11B of 21.2‰, and 87Sr/86Sr of 0.70840. The waters from the study district show a systematic increase in major, trace element and TDS concentrations and δ11B values along the pathway of groundwater migration which can only be interpreted in terms of water–rock interaction at depth and strong surface evaporation. The hydrochemical and isotopic data presented here confirm that the groundwaters in the Shihongtan ore district are the combined result of migration, water–rock interaction and mixing of meteoric water with connate waters contained in sediments.  相似文献   

13.
The 1.27 Ga old Ivigtut (Ivittuut) intrusion in South Greenland is world-famous for its hydrothermal cryolite deposit [Na3AlF6] situated within a strongly metasomatised A-type granite stock. This detailed fluid inclusion study characterises the fluid present during the formation of the cryolite deposit and thermodynamic modelling allows to constrain its formation conditions.Microthermometry revealed three different types of inclusions: (1) pure CO2, (2) aqueous-carbonic and (3) saline-aqueous inclusions. Melting temperatures range between − 23 and − 15 °C for type 2 and from − 15 to − 10 °C for type 3 inclusions. Most inclusions homogenise between 110 and 150 °C into the liquid.Stable isotope compositions of CO2 and H2O were measured from crushed inclusions in quartz, cryolite, fluorite and siderite. The δ13C values of about − 5‰ PDB are typical of mantle-derived magmas. The differences between δ18O of CO2 (+ 21 to + 42‰ VSMOW) and δ18O of H2O (− 1 to − 21.7‰ VSMOW) suggest low-temperature isotope exchange. δD (H2O) ranges from − 19 to − 144‰ VSMOW. The isotopic composition of inclusion water closely follows the meteoric water line and is comparable to Canadian Shield brines. Ion chromatography revealed the fluid's predominance in Na, Cl and F. Cl/Br ratios range between 56 and 110 and may imply intensive fluid–rock interaction with the host granite.Isochores deduced from microthermometry in conjunction with estimates for the solidification of the Ivigtut granite suggest a formation pressure of approximately 1–1.5 kbar for the fluid inclusions. Formation temperatures of different types of fluid inclusions vary between 100 and 400 °C. Thermodynamic modelling of phase assemblages and the extraordinary high concentration in F (and Na) may indicate that the cryolite body and its associated fluid inclusions could have formed during the continuous transition from a volatile-rich melt to a solute-rich fluid.  相似文献   

14.
This paper describes unusual graphite–sulfide deposits in ultramafic rocks from the Serranía de Ronda (Spain) and Beni Bousera (Morocco). These deposits occur as veins, stockworks and irregular masses, ranging in size from some centimeters to a few meters in thickness. The primary mineral assemblage mainly consists of Fe–Ni–Cu sulfides (pyrrhotite, pentlandite, chalcopyrite and cubanite), graphite and chromite. Weathering occurs in some sulfide-poor deposits that consist of graphite (up to 90%), chromite and goethite. Texturally, graphite may occur as flakes or clusters of flakes and as rounded, nodule-like aggregates. Graphite is highly crystalline and shows light carbon isotopic signatures (δ13C≈− 15‰ to − 21‰). Occasionally, some nodule-like graphite aggregates display large isotopic zoning with heavier cubic forms (probably graphite pseudomorphs after diamond with δ13C up to − 3.3‰) coated by progressively lighter flakes outwards (δ13C up to − 15.2‰).Asthenospheric-derived melts originated the partial melting (and melt–rock reactions) of peridotites and pyroxenites generating residual melts from which the graphite–sulfide deposits were formed. These residual melts concentrated volatile components (mainly CO2 and H2O), as well as S, As, and chalcophile elements. Carbon was incorporated into the melts from the melt–rock reactions of graphite-bearing (formerly diamonds) garnet pyroxenites with infiltrated asthenospheric melts. Graphite-rich garnet pyroxenites formed through the UHP transformation of subducted kerogen-rich crustal material into the mantle. Thus, graphite in most of the studied occurrences has light (biogenic) carbon signatures. Locally, reaction of the light carbon in the melts with relicts of 13C-enriched graphitized diamonds (probably generated from hydrothermal calcite veins in the subducting oceanic crust) reacted with the partial melts to form isotopically zoned nodule-like graphite aggregates.  相似文献   

15.
The calcite cement in the Lower Ordovician Majiagou Formation in the Ordos basin in northern China can be subdivided into three groups based on preliminary results of oxygen and carbon isotopes and fluid inclusion microthermometry. Group 1 has low oxygen isotopes (− 14‰ to − 18‰), low Th values (92–103 °C), and low salinities (1.7–4.9 wt.% NaCl equivalent) and is interpreted to have precipitated during early burial from porewater influenced by meteoric water. Group 2 has much higher oxygen isotope values (− 5‰ to − 8‰), which, coupled with the higher Th values (136–151 °C), suggest that the calcite was precipitated from fluids that were significantly enriched in 18O, possibly resulting from fluid–rock reaction during burial. Group 3 occurring along fractures is characterized by high salinities (21–28 wt.% NaCl equivalent) and is interpreted to have been precipitated from locally preserved residual evaporitic brines. The occurrence of primary hydrocarbon inclusions and its low carbon isotopes (− 11‰ to − 15‰) suggest that precipitation of group 3 calcite took place in the presence of hydrocarbons.  相似文献   

16.
Regional oxygen isotopic sytematics have been performed mainly on the felsic volcanic footwall rocks of the orebodies but also on purple schist characteristic of the hanging wall series, around two giant VMS deposits in the Spanish Iberian Pyrite Belt, Riotinto and La Zarza. As the terranes of the Iberian Pyrite Belt, these two giant deposits have been affected by the Hercynian tectono-metamorphic events, strongly modifying their geometry. About 60 and 40 samples were collected over a 10×4 km2 area at Riotinto and a 3×2 km2 area at La Zarza, respectively. Whole-rock powders were analysed for oxygen by CO2-laser fluorination. At both sites, a same type of low-δ18O anomaly down to +3.6‰, well differentiated from the regional background (up to 20‰), was identified near the orebodies. The lowest δ18O values (+4 to +11‰) correspond to the chlorite hydrothermal halo, essentially restricted to the feeder zones of the orebody. Intermediate δ18O values (+9 to +15‰) correspond to the sericite hydrothermal halo, mostly developed laterally to the orebody until 0.5–1 km. The regional background (+16 to +20‰) is represented by spilitised volcanic rocks. A same kind of low anomaly, but with less contrast, was defined in purple schist in the immediate hanging wall of the orebodies. All these results demonstrate that, despite high geometrical modifications of the orebodies related to the Hercynian tectonics, oxygen isotopic anomalies recorded by volcanic host rocks during the emplacement of the mineralising hydrothermal systems are still identified. This strongly suggests that oxygen isotopic systematics could be useful to identify target areas in the Iberian Pyrite Belt, as already demonstrated on other VMS targets in the world.  相似文献   

17.
Miocene igneous rocks (diorites, andesites, dacites, rhyolites and microgranites) of Chetaibi and Cap de Fer massif, NE Algeria, are high-K calc-alkaline to shoshonitic rocks. Fresh diorites have δ34S and δ18O values ranging between −2.5‰ and +5.9‰, +6.5‰ and +6.7‰ respectively, indicating a mantle origin. The relatively low δ34S values (−5.4‰ to −12.2‰) and high δ18O (+8.3‰ to +9.0‰) of altered diorites indicate the input of a crustal component to the initial magma. The microgranites’ I-type signature is indicated by the geochemical data and the δ34S and δ18O values of −1.2‰ and −3.6‰, and +7.8‰ to +10.4‰ respectively. The andesites show a large variation of δ34S, between −33.2‰ and +25.7‰. Massive andesites with δ34S between +6.8‰ and +7.6‰ preserve a 34S-enriched mantle signature. The δ34S of the lava flows between +25.7‰ and +25.8‰ are attributed to open system magma degassing, whereas the low δ34S of two andesitic dyke samples (−13.7‰ and −33.2‰) strongly suggest a crustal sulphur input. High δ18O (+9.2‰ to +15.7‰) of andesites indicate post-magmatic alteration (mainly silicification); the flyschs with δ18O between of +13.3‰ and +21.7‰ are most likely the contaminant. Quartz veins within the andesites gave a δ18O value of +23.0‰ while silica-filling vesicles yielded a value of +13.8‰. Initial Sr-isotope data are rather high for all the rocks (diorites: 0.707–0.708, andesites: 0.707–0.710, and microgranites and rhyolites: 0.717–0.719), and because geochemical and stable isotope data do not indicate a substantial amount of crustal assimilation, an extensive enrichment of the mantle source by subducted sediments is called for. A metasomatized-mantle source, characterized by high radiogenic Sr and relatively high δ18O, has also been indicated for the genesis of similar Tertiary igneous rocks in the Western Mediterranean basin, e.g. the Volcanic Province of southeasten Spain [Benito, R., Lopez-Ruiz, J., Cebria, J.M., Hertogen, J., Doblas M., Oyarzun, R., Demaiffe, D., 1999. Sr and O isotope constraints on source and crustal contamination in the high-K calc-alkaline and shoshonitic neogene volcanic rocks of SE Spain. Lithos 46, 773–802] and some plutons of northeastern Algeria [Ouabadi, A., 1994. Pétrologie, géochimie et origine des granitoïdes peralumineux à cordiérite (Cap Bougaroun, Béni-Touffout et Filfila), Algérie nord-orientale. Thèse de Doctorat, Université de Rennes I, France, 257p; Fourcade, S., Capdevila, R., Ouabadi, A., Martineau, F., 2001. The origin and geodynamic significance of the Alpine cordierite-bearing granitoids of northern Algeria. A combined petrological, mineralogical, geochemical and isotopic (O, H, Sr, Nd) study. Lithos 57, 187–216].  相似文献   

18.
Coal-derived hydrocarbons from Middle–Lower Jurassic coal-bearing strata in northwestern China are distributed in the Tarim, Junggar, Qaidam, and Turpan-Harmi basins. The former three basins are dominated by coal-derived gas fields, distributed in Cretaceous and Tertiary strata. Turpan-Harmi basin is characterized by coal-derived oil fields which occur in the coal measures. Based on analysis of gas components and carbon isotopic compositions from these basins, three conclusions are drawn in this contribution: 1) Alkane gases with reservoirs of coal measures have no carbon isotopic reversal, whereas alkane gases with reservoirs not of coal measures the extent of carbon isotopic reversal increases with increasing maturity; 2) Coal-derived alkane gases with high δ13C values are found in the Tarim and Qaidam basins (δ13C1: − 19.0 to − 29.9‰; δ13C2: − 18.8 to − 27.1‰), and those with lowest δ13C values occur in the Turpan-Harmi and Junggar basins (δ13C1: − 40.1 to − 44.0‰; δ13C2: − 24.7 to − 27.9‰); and 3) Individual specific carbon isotopic compositions of light hydrocarbons (C5–8) in the coal-derived gases are lower than those in the oil-associated gases. The discovered carbon isotopic reversal of coal-derived gases is caused by isotopic fractionation during migration and secondary alteration. The high and low carbon isotopic values of coal-derived gases in China may have some significance on global natural gas research, especially the low carbon isotope value of methane may provide some information for early thermogenic gases. Coal-derived methane typically has much heavier δ13C than that of oil-associated methane, and this can be used for gas–source rock correlation. The heavy carbon isotope of coal-derived ethane is a common phenomenon in China and it shed lights on the discrimination of gas origin. Since most giant gas fields are of coal-derived origin, comparative studies on coal-derived and oil-associated gases have great significance on future natural gas exploration in the world.  相似文献   

19.
Black and white dolomite crystals (mm to cm width) of different isotopic composition are associated with Triassic diapirism in central Tunisia, as well as with evaporite minerals and clays. The white dolomites occur mostly in the Jabal Hadifa diapir near the contact with Cretaceous limestones, whereas the smaller black dolomites occur in the Jabal Hamra diapir. The former dolomite has a narrow range of δ18O and δ13C values (− 3.83‰ to − 6.60‰ VPDB for δ18O; − 2.11‰ to − 2.83‰ VPDB for δ13C), whereas the latter dolomite has a wider range and more depleted values (− 4.92‰ to − 9.97‰ for δ18O; − 0.55‰ to − 6.08‰ for δ13C). However, the 87Sr / 86Sr ratios of most of the samples are near Triassic seawater values. Dolomite formation is due to at least two different fluids. The main fluid originated from deeper hydrothermal or basinal sources related to the Triassic saliferous rocks and ascended through faults during the diapiric intrusion. The second, less important fluid source is related to meteoric water originating from Cretaceous rocks.  相似文献   

20.
The possible contamination of a groundwater system with industrial wastewater originating from a paper mill factory has been investigated in Piteå, N. Sweden. Six samples were collected from the wastewater in the waste dump and twelve samples from the adjacent groundwater were analyzed for chemistry and sulfur isotopes. The industrial wastewater is a saline water consisting mainly of Na–HCO3–SO4, having a high pH and showing δ34S values between 7‰ and 9‰ affected by bacterial sulfate reduction. The groundwaters are relatively dilute, dominated by Na+, Ca2+ and HCO3−, but with varying concentrations as exemplified by sulfate with concentrations varying between 3 and 69 mg L− 1 while the δ34S values range from − 0.5‰ to 14.3‰. The data suggest that the main S sources in the waters are the bedrock sulfides and/or atmospheric deposition, which, sometimes, are overlapped by bacterial sulfate reduction. Contamination from the waste dump does not occur.  相似文献   

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